1. Field of the Invention
The present invention relates to a control system for an apparatus having a permanent split capacitor (PSC) motor and more particularly to a control for an automatic washing machine having a reversing PSC motor wherein the operations of the washing machine are controlled in response to phase angles of the motor determined from sensed zero crossings of current flowing through the motor's windings.
2. Description of the Prior Art
A control system for various appliances having an AC induction drive motor including an automatic washing machine is shown in my U.S. Pat. No. 4,481,786. That control system employs a ferrite core sensor having a primary winding that is formed of two turns of the drive motor's run winding, the sensor having a single turn secondary winding that forms a sense winding coupled to a motor phase monitoring circuit. The sense winding provides a signal representing a polarity change in the run winding current. The current polarity change signal is used by the motor phase monitoring circuit to provide a voltage compensated motor phase angle pulse to a microcomputer for the appliance to control various operations of the appliance. More particularly, a digital representation of the motor phase angle pulse is used by the microcomputer to monitor the starting of the drive motor by detecting a characteristic decrease in the motor phase angle representation. The motor phase angle representation is further used by the microcomputer of an automatic washing machine to determine the agitator torque which is in turn used by the microcomputer to automatically control the water level of the washing machine. An average motor torque number is also determined from the motor phase angle representation wherein the average motor torque number is used to provide an end of drain control for the washing machine.
It has been found that automatic washing machines having reversing PSC drive motors cannot be as accurately controlled by the control system shown in U.S. Pat. No. 4,481,786 as washing machines having AC induction motors because the motor start time of a PSC motor varies not only with the size of the clothes load but with variations in the installation line voltage. More particularly, for a washing machine having a reversing PSC motor, the line voltage affects the motor start time more than the size of the clothes load. Further, the motor phase angle of a PSC motor does not change in the same manner as the motor phase angle of an AC induction motor since there is not a characteristic decrease in the phase angle of the PSC motor indicative of the motor reaching its operating speed. Another difference between washing machines having an AC induction motor and washing machines having a PSC motor is that the stroke angle and stroke rate of an agitator driven by an AC induction motor is fixed; whereas, the stroke angle and stroke rate of an agitator driven by a reversing PSC motor is variable.